I suppose you already used a cleaning tool like:
Install it to your desktop.
1. Open CCleaner.
2. Place a check by everything in the Applications tab.
3. Place a check by Internet Explorer, Windows explorer, and System in the Windows tab (take care that Windows logfiles is unchecked).
4. Hit the button that says Run CCleaner
5. Reboot to remove index.dat files.
Also try this:
Go to Start > Run
Type: ipconfig /flushdns
Please go to Start -> Control Panel, and choose Network Connections.
Then right click on your default connection, usually Local Area Connection or Dial-up Connection if you are using Dial-up, and left click on properties. Double-click on the Internet Protocol (TCP/IP)
item and select the radio button that says Obtain DNS servers automatically
. Click OK twice, and restart your computer.